[PATCH 07/39] scsi: avoid useless free_list lock roundtrips

Christoph Hellwig
2014-03-17T13:27:40Z

[-- Attachment #1: 0007-scsi-avoid-useless-free_list-lock-roundtrips.patch --]
[-- Type: text/plain, Size: 1134 bytes --]

Avoid hitting the host-wide free_list lock unless we need to put a command
back onto the freelist.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Hannes Reinecke <hare@suse.de>
---
drivers/scsi/scsi.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index d8afec8..fb86479 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -320,13 +320,14 @@ void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd,
{
unsigned long flags;

- /* changing locks here, don't need to restore the irq state */
- spin_lock_irqsave(&shost->free_list_lock, flags);
if (unlikely(list_empty(&shost->free_list))) {
- list_add(&cmd->list, &shost->free_list);
- cmd = NULL;
+ spin_lock_irqsave(&shost->free_list_lock, flags);
+ if (list_empty(&shost->free_list)) {
+ list_add(&cmd->list, &shost->free_list);
+ cmd = NULL;
+ }
+ spin_unlock_irqrestore(&shost->free_list_lock, flags);
}
- spin_unlock_irqrestore(&shost->free_list_lock, flags);

if (likely(cmd != NULL))
scsi_pool_free_command(shost->cmd_pool, cmd);
--
1.7.10.4